This invention relates to an electrocardiographic waveform display apparatus and a method of expressing electrocardiographic waveforms in which a plurality of electrocardiographic waveforms are expressed in a time series.
As an example of the prior art, an apparatus as disclosed in the specification of Japanese Patent Application Laid-Open No. 57-81329 is designed to record electrocardiographic waveforms continuously over an extended period of time and subsequently reproduce the recorded waveforms so that any changes therein can be distinguished, thereby making it possible to discover heart ailments and to accurately identify the status thereof. Some of these conventional apparatus are designed to record for a period of 24 hours or longer.
Apparatus for the purpose of reading and visually displaying the recorded waveforms mainly employ any of the following three methods to display the recorded waveforms:
(1) a method in which recorded waveforms are compressed and then continuously recorded or displayed;
(2) a method which places emphasis on the fact that an ST waveform contained in the electrocardiographic waveforms is of great importance in judging the presence of heart disease, and which displays the ST waveform on a CRT screen by a superimposing technique using R-wave synchronization; and
(3) a method of providing a trend display at any measurement point.
However, method (1) is disadvantageous in that the recorded waveforms are small and it is difficult to accurately recognize the ST portion. Method (2) makes it possible to recognize changes over several beats only and the method does not lend itself to recording on paper or the like. With method (3), only a change in the ST portion at specific point can be determined, thus making it impossible to accurately judge an entire waveform.